Method of and apparatus for correcting the lead error of screw threads



Jan. 26, 1943. c. A. BICKEL 2,309,299

METHOD OF AND APPARATUS FOR CORRECTING THE LEAD ERROR OF SCREW THREADS Filed Nov. 18, 1940 3 Sheets-Sheet l FIEr. E

INVENTOR CUFFORD A. BICKEL ATTORNEYS Jan. 26, 1943. c. A. BLCKEL METHOD OF AND APPARATUS FOR CORRECTING THE LEAD ERROR OF SCREW THREADS Filed Nov. 18, 1940 3 Sheets-Sheet 2 Jan. 26, 1943. c. A. BICKEL 2,309,2 9

' METHOD OF AND APPARATUS FOR CORRECTING THE LEAD ERROR OF SCREW THREADS Filed Nov. 18, 1940 3 Sheets-Sheet 3 INVENTOR CLIFFORD A n L Patented Jan. 26, 1943 METHOD OF AND APPARATUS FOR COB- RECTING THE LEAD ERROR OF SCREW THREADS cmrm-d a. Bickel, Sidney, Ohio, assignor to The Monarch Machine Tool 00., Sidney, Ohio, a

corporation of Ohio Application November 18, 1940, Serial No. 366,099

11 Claims. (Cl. 82-5) This invention. relates to thread chasing, and in particular to means for correcting lead errors in thread chasing.

It is common knowledge that most lead screws in lathes, grinding machines and other machine tools vary more or less in lead throughout their length, and that although these variations may be relatively small, they will be translated to and appear increased in lead screws generated on such machines. Variou devices have been designed to cope with this difliculty but the results have not been fully satisfactory since lead errors in thread chasing not only result from inaccuracies in the master lead screw but are due to many variable factors such as temperature variations, changes in the material to be chased and deilections caused by work stresses and strains between the work and the cutting tool and between the various moving and guiding parts.

It is an object of the invention to provide a lead error correcting device which is simple in operation and construction and easily attachable to a machine tool without impeding the work to be done on said machine tool.

Still another object consists in the provision of a lead error correcting device which will allow of every lead error being corrected while or before the finishing cut is made on the thread to be chased.

It is a still further object of the invention to provide a lead error correcting device which will be operable to move the lead screw 01 the machine tool on which the thread is chased in accordance with the lead errors appearing in said thread, for correcting said errors.

It is another object of the invention to provide a lead error correcting device as set forth in .the preceding paragraph, in which the movement of the lead screw of the machine tool is translated to indicating means to enable control of the lead screw movement.

These and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawings, in which:

Figure l is an elevation of a portion of a lathe having attached .thereto a lead error correcting device according to the invention.

Figure 2 is a top view of Figure 1.

Figure 3 is a longitudinal section through .the lead error correcting device along the line 3-3 of Figure 2.

Figure 4 illustrates partially in section the gear box or drive end oi the lead screw showing the means of compensating for the changes-in length due to the advancing and retarding of the lead screw.

Figure 5 is a partial section along the line 55 of Figure 2.

General arrangement According to the present invention the lead screw of the machine tool on which a thread is to be chased is associated with a shifting mechanism which is adapted to move the lead screw of the machine tool longitudinally selectively in one or the other direction by minute distances. The amount by which the lead screw is shifted is checked by an indicating mechanism connected to the machine tool.

After a rough cut on the screw to be chased on the machine tool has been made, the lead of the screw to be cut is tested by a testing device,v for instance a nut or a thread feeler in cooperation with an indicating mechanism, to determine the diil'erences between the actual lead on the screw to be chased and the lead it should have. These differences are marked down, while .the locations where the said differences occur are noted. When this testing operation has been finished, the testing mechanism is disengaged from the thread to be chased and the finishing cut is made on the said thread,

while whenever the cutting tool. reaches a posi- .tion on the thread where, as previously determined by-the testing operation, the actual lead differs from the desired lead, the lead screw of the machine tool is shifted to the left or the I right in accordance with the test data obtained by the testing operation. The cutting toolwill then move in a path so as to perform a uniform accurate lead, thereby correcting the inaccura cies of the rough cut.

Structural arrangement Referring to the drawings in detail, i0 is the bed of a lathe with a head stock II, a tail stock I! and a lead screw l3. Carried by the spindle in the head stock II is a chuck ll which supports one end of a screw l5 to be cut, the other end oi which is supported by the center IS in the tail stock l2. However, if desired, the screw to be cut may of course be mounted between two centers. The tool H for chasing the thread is carried by a swivel l8 and the transverse slide l9, supported. by the part 20 of the carriage 2|, which may either be moved automatically or by rotation 01 the handwheel 22. I05 is a handwheel for effecting the longitudinal shitting movement of the lathe lead screw H which shiftingmovement may be checked by the indicating mechanism 28.

A tape reel (not shown) of the spring return type is associated with the end of the lathe and has mounted thereon a steel tape 25, one end of which is connected with the tape reel, while its other end is connected with the carriage 2| at-=the point 28. The tape is, in this way, held under suitable tension for correct reading and calibration. The tape 25 is passed through a sight member 21 which preferably magnifies ,the calibration on the tape soas to allow the most accurate reading.

Connected to the lathe bed I8 is the rear lead screw box 28 having a flange 28 integral therewith which supports the compensator housing 88. The lead screw I8 extends through the rear lead screw box 28 and the compensator housing 88 and is supported in the rear lead screw box 28 by a bearing 8|. The bearing 8| is held in position by a snap ring 82 and a deflector bushing 88 connected in any convenient manner with the rear lead screw box 28, for instance, by a screw 84. The lead screw I8 is free to slide longitudinally in the bearing 8 I.

The lead screw I8 has extensions 85 and 88, of which the extension 85 has mounted thereon thrust bearings 81 and 88, while the extension 88 is provided with a thread 88. Mounted between the thrust bearing 81 and the shoulder 48 of the lead screw I8 is a disc 4|. The thrust bearings 81 and ,88 are spaced from each other by a compensating screw 42 and held in their position by the disc 4| engaging the shoulder 48 and the spacing collar 48 pressed against the thrust bearing 88 by means of the adjusting nut 44 and lock nut 45 threaded on the thread 88.

The compensating screw 42 is prevented from rotating by means of a key 48 engaging the head portion 41 of the compensating screw 42 and the rear lead screw box 28.

Meshing with .the compensating screw 42 is a nut 48 keyed by means of a key 48 to the hub portion 58 of the worm wheel 8|. The hub portion 58 may be connected with the worm wheel 5|- in any convenient manner,'for instance by screws 52. To prevent longitudinal movement between the hub portion 58 and the nut 48, the latterjs connected to the hub portion 58 by means of a screw 58. The compensating screw 42 is furthermore engaged by a nut 84 spaced from the nut 48 and keyed by means of the key 55 to the hub portion 58. In contradistinction to the nut 48, however, the nut 54 is not rigidly connected to the hub portion 58. The nut 54 is held in its position by means of the threaded bushing 58 provided with a thread 51. which engages a corresponding thread 58. The bushing 58 may be adjusted relative .to the hub portion 88 and when in desired position, maintained therein by tightening the set screw 58. The arrangement of the nut 54 and the bushing 58 is merely for preventing any play between the compensating screw 42 and the nut 48 when the latter'is rotated by rotation of the worm wheel 5|. 7

The gear hub portion 58 is rotatably mounted in the compensator housing 88 by means of antifriction bearings 88 and 8|, spaced from each 7 other by sleeves 82 and 88. The sleeve 82 is connected to the compensator housing 88 by means of the screw 84, while the sleeve 88 is held in its position due to the fact that the inner race ring of the anti-friction bearing 8| abuts the shoulder 85 of the hub portion 88, whereas the inner race ring of the anti-friction bearing asoasee 88 is pressed against the sleeve 88 by means of the nut 88, held in its position by the set screw 81.

As will be cleargfrom the above, turningmovement of the worm wheel 5| will cause rotation of the nut 48 which, due to the fact that the key 48 prevents rotation of the compensating screw 42, will result in a longitudinal movement of the screw 42 and, thereby, of the lead screw I8, which is longitudinally movable in the bearing 81. The other end of the lead screw I8 (Figure 4) adjacent the head stock II of the lathe is rigidly connected to the bushing 88 by means of pin 88.

The bushing 88 has a splined portion 18, engaging a correspondingly splined member 1| connected by any convenient means, for instance a pin 12, with the stepped shaft 18. In this way relative movement between the lead screw I8 and the shaft 18 is made possible.

Pressed into the bore 14 of the splined bushing 88 is a bushing 15, preferably of bronze, bearing on the projection 18 of the stepped shaft 18. The stepped shaft 18 is journalled in antifrictlon bearings 11 and 18. surrounded and spaced by the cylinder 18 which, by means of the flange 88, is connected to the gear box 8|. The outer end of the cylinder 18 is closed by a cover 82. Keyed to the shaft 18, by means of key 88, is a gear 84 adapted to mesh with one of the gears in the gear box 8| for transmitting the drive thereof to the lead screw I8.

Meshing with the worm wheel II is .a worm 88 (Figure 5) keyed to the worm shaft 88 by means of keys 81.

' in anti-friction bearings 88, 88 and 88 housed in the worm housing 8| which is provided with a flange portion 82. The anti-friction bearings 88. 88 and 88 are positioned by the sleeves 88, 84 and collars 85 and 88. The worm housing 8| is closed at its lower end by a cover 81- connected thereto by means oi screws 88.

Keyed to the worm shaft 88 by a key 88 is a collar I88 having a hub portion III'integral therewith and being provided with an annular r-slot I82. The annular T-slot I82 is engaged by bolts I88 provided with a T-head and passing ment of the T-slot bolts "8 makes it possible to circumferentially adjust the handwheel with regard to the pointer I88 so as to set the zero calibration on the rim of the handwheel I85 in line with the pointer I88. I

The calibrations on the handwheel I85 may be in any desired increments, for instance in one ten-thousandth of an inch and may, for example, register from zero plus or minus twenty-five ten-thousandths of an inch. The calibrations on the handwheel I85 are eifective when the lead errors of the screw being chased are all negative or all positive. However, due to the back lash and stresses in all of the working parts from the compensating handwheel I85 to the cutting tool, the graduations are not effective when opposite errors, i. e. positive and negative errors are corrected during one and the same correcting oper- The worm shaft 88 is iournalledation. Therefore, in this instance, the indicating mechanism 24 is used.

As will be seen from Figure 3, the indicating mechanism 24 is provided with a contactor IIII, which is engaged by a contacting screw III held by the lock nut H2 in the end of the lead screw I3. The indicating mechanism 24 is supported by a bracket I I 3, adjustably connected by means of a knurled thumb screw 4 with the cover H5 attached to the compensator housing 30 in any convenient manner. The contactor I III is constantly urged into engagement with the screw I I I so that the shifting movement of the lead screw IS in either direction will be translated to the indicating mechanism 24, thereby permitting an accurate shifting movement of the lead screw I3.

To secure proper meshing between the worm B5 and worm wheel 5|, the worm housing 9| is pivotally connected to the compensator housing 30 by means of the stud H6 so that it can be shifted thereabout and then secured in its desired Operation It may be supposed that the screw It has been rough chased to a desired degree so as to fit a gauging nut, a feeler, or any other convenient means, which is associated with the lead testing device. Such lead testing devices are well known to those skilled in the art and substantially comprise feeling means which feel the lead and, when moved through a lead, indicate by means of a pointer, the difference between the tested lead and the desired lead.

The lead testing device is now mounted on the carriage 2i and the free end of the tape 25 is also attached to the carriage 2i. It may be assumed, for instance, that a screw with a pitch of 6mm. is to be chased, which means that the lead of the lead screw should be 6mm. per one revolution of the screw I5. If it is desired to check every four threads of the screw I5, the latter is now rotated by four complete revolutions. To be sure that the revolutions are complete and accurate, a 360 degree dial may be associated with the screw I5 and cooperate with a mark on the said screw. If the screw in the present instance has been rotated by four complete revolutions, the total lead should be 24mm. The testing device will then indicate the difierence between the said 24mm. and the actual total lead on the screw I5 for the respective four revolutions thereof. This difference is marked down, while the tape 25 is provided with a mark to indicate the location of the point on the screw I5 at which the said difference is to be found. Thereupon the testing device is slightly moved to such a position that its indication corresponds to the desired pitch and now the screw I5 is again rotated by four complete revolutions and the testing operation repeated.

After the testing operation has been finished, the testing device is removed from thecarriage 2| and the operator starts the correcting cut on the screw l5 which, if desired, may be the finishing cut. While this cut is being carried out, the handwheel I05 is adjusted whenever a point marked on the tape 25 is reached, so that the lead screw I3 is moved by a distance in correspondence to the error previously determined at the position corresponding to the marking on the tape.

If all errors are positive or negative, the handwheel I05 will be fully eflective after the zero mark of it's calibration has been brought into alignment with the pointer III, as previously explained, in order to prevent any back lash or play between the handwheel III and the compensating screw 42. It alternately positive and negative errors are to be corrected, the handwheel I05 has to be adjusted in accordance with the indication on the indicator 24.

From the above it will be clear that according to the present invention the error in the pitch of the screw to be chased is directly checked and corrected on said screw in contrast to previous methods which locate and correct each factor separately which may cause a lead or pitch error.

It will be understood that I desire to comprehend within my invention such modifications as come within the scope of the claims and the invention.

Having thus fully described my invention what I claim as new and desire to secure by Letters Patent is:

1. In a machine tool, alead screw operable for thread chasing, means for axially moving said lead screw, indicating means adapted automatically to indicate the magnitude of the longitudinal movement of said lead screw, and translating means interposed between said lead screw and said indicating means for translating the axial movement ofsaid lead screw to said indicating means.

2. In a machine tool, a lead screw operable for thread chasing, means for axially moving said lead screw, indicating means adapted automatically to indicate the magnitude of the longitudinal movement of said lead screw, translating means interposed between said lead screw and said indicating means for translating the axial movement of said lead screw to said indicating means, and means for adiusting said translating means to vary the translating operation thereof.

3. In a machine tool, a lead screw operable for thread chasing, means for axially moving said lead screw, indicating means adapted automatically to indicate the magnitude of the longitudinal movement of said lead screw, a casing housing a portion of said lead screw, and means for adjusting the location of said indicating means relative to said casing.

- 4. In a machine tool, a lead screw operable for thread chasing, means for axially moving said lead screw, means for effecting a predetermined.

and variable axial movement of said lead screw, a carriage movable substantially parallel to said lead screw and adapted to support a cutting tool, and a calibrated reeled tape having one end thereof connected to said carriage.

5. In a machine tool, a lead screw operable for thread chasing, means for axially moving said lead-screw, means for eifecting a predetermined and variable axial movement of said lead screw, a carriage movable substantially parallel to said lead screw and adapted to support a cutting tool, optic means, and a calibrated reeled tape passing by said optic means and having one end connected to said carriage.

6. In a machine tool, a lead screw operable for thread chasing. a screw and nut arrangement operable for shifting said lead screw in axial direction, a pointer, and a calibrated handwheel for actuating said screw and nut arrangement, said handwheel and said pointer being movable relative to each other. v

7. In a machine tool, a lead screw operable for thread chasing, a screw and nut arrangement operable for shifting said lead screw in axial direction, a stationary pointer, and a calibrated handwheel rotatable for actuating said screw and nut arrangement, said calibration on said handwheel being adjustable relative to said pointer.

3. In a machine tool, a lead screw operable for thread chasing, a nut and screw arrangement for axially shifting said screw in either direction, a worm wheel operatively connected with said nut and screw arrangement, a worm adapted to mesh with said worm wheel, means for operating said worm, and a casing housing said worm, said casing being pivotally mounted so as to vary the engagement of said worm with said worm wheel. 9. In a machine tool, a lead screw operable for thread chasing, means for rotating said lead screw, a carriage for supporting a. thread chasing tool, means responsive to a rotationof said lead screw for moving said carriage in the direction of the longitudinal axis of said lead screw, a screw and nut arrangement adapted to efiect axial movement of said lead screw together with said carriage as a. unit in either direction independently of a rotation of said lead screw, means for preventing play between said screw and nut aeoaaee arrangement, and means for selectively actuat ing said screw and nut arrangements iii. In a machine tool, a lead screw operable for thread chasing, anti-friction bearing means rotatably supporting one end of said lead screw, a screw arranged between said bearing means, two nuts spaced from each other and meshing with said screw, a worm wheel having a hub rigidly connected with one of said nuts, while the other nut is rotatably connected with but slidable relative to said hub, and means for actuating said worm wheel to axially move said lead screw together with said anti-friction bearings.

11. In a machine tool, a lead screw operable for thread chasing, splined means rigidly connected with one end of said lead screw, means slidably engaging said splined means for guiding the same, bearing means supporting the other end of said lead screw and adapted to allow axial movement thereof in said bearing means, and means for axially moving said lead screw in either direction by a predetermined distance.

CLIFFORD A. BICKEL. 

